The present invention relates to electronic musical instruments and, in particular to an apparatus for automatically providing an accompaniment.
An automatic accompaniment apparatus that performs an accompanimental line such as bass, obbligato in combination with a melody is known. Such apparatus generally includes a memory which stores an accompaniment pattern data forming the basis of the accompanimental line. The pattern consists of horizontal or time information indicating when tones should be sounded and vertical information about the accompanimental line. According to chord information supplied by a player via a musical performance input unit such as a keyboard, the vertical information of the accompanimental line is converted into a succession of pitches.
In one prior art accompaniment apparatus, the vertical information is formed with data specifying pitch ordinal locations of a plurality of input notes forming a chord. In operation, the location specifying data in the accompaniment pattern are respectively converted into corresponding pitches of chord notes. While the apparatus can provide an accompanimental line in inversions by inputting a chord in corresponding positions by means of the musical performance unit, it cannot produce tones other than the input chord members because of the principles of the apparatus. An example of the apparatus of this type is disclosed in Yamaga et al U.S. Pat. No. 4,217,804 issued on Aug. 19, 1980.
In another prior art apparatus, the vertical information of accompaniment pattern is given by stored data each specifying a pitch interval or distance from the root of chord. The interval specifying data are changed depending on the type of chord. For example, if a minor chord is designated, the data element specifying (major) third scale degree above the root is lowered by a half step and then added to the root of the minor chord to define the final pitch. Whereas the apparatus of this kind can provide an accompanimental line containing nonharmonic tones, it cannot guarantee that the produced nonharmonic tones are always proper or desirable in terms of music. Let a diatonic scale be available for chords such as major and minor. Under the assumption, a data element specifying second scale degree above the root is always converted into a pitch higher than the root by major second (three semitones) whenever a major or minor chord is provided. Therefore, each time the root of chord varies, the pitch of nonharmonic tone will change in parallel. This will lose the sense of key in the accompanimental line.